We hypothesize that small molecules that readily enter cells can induce nonsense suppression by the protein synthetic apparatus such, that nonsense mutations are translationally bypassed at levels up to 20 percent. Evaluation of efficacy will be performed with the prototype drug gentamicin, an aminoglycoside antibiotic. If successful, translational bypass therapy could be beneficial for a significant minority of patients with severe genetic disease. Hemophilia is chosen as the model disease. Major effects of severe hemophilia A)B can be eliminated with only a slight increase in factor level. The hemophilias are an advantageous system to determine directly the efficacy of gentamicin gene therapy because many patients with nonsense mutations are available, the protein product can be measured readily and the kinetics of accumulation and decay can be determined over a short period since the proteins turn over rapidly. The proposed study has four specific aims: 1.Assess gentamicin suppression of nonsense mutations in an initial set of ten patients with severe hemophilia B. 2.Determine if there is a correlation between gentamicin-induced nonsense suppression and gene (factor VIII or IX), stop codon type, and sequence context. 3.Determine whether gentainicin suppresses frameshift mutations in five patients with hemophilia A or B and missense mutations in five patients with hemophilia A or B. 4.Determine whether the effect of gentamicin can be maintained with regular administration of gentamicin for up to twelve weeks. Nonsense suppressors could revolutionize therapy for hemophilia in underdeveloped countries where factor replacement is not readily available and carries risks of blood-borne pathogens. An efficacious nonsense suppressor should be effective in nonsense mutations in any of the 30,000 -40,000 human genes. Nonsense suppressors also may be beneficial in the treatment of cancers that result from nonsense mutation in tumor suppressor genes.